Devices of the present nature have been known, e.g. as disclosed in German DE-AS No. 25 03 742. In these known devices, the connecting steel reinforcements are isolated in a housing device which is constructed as a box shaped structure of foam plastic. When a joint area, for example, a T-shaped butt joint between a previously poured concrete wall and a subsequently poured concrete wall, at a right angle thereto is to be prepared, after the known housing device has been integrally cast into the previously poured concrete wall it is necessary to remove the foam plastic in order to bend the connecting portions of the steel reinforcements outwardly for attachment to the subsequently poured wall. In particular, the steel reinforcements themselves must be completely free of foam plastic, since an inadequate joining of steel and concrete will result if that is not done. This requires a considerable amount of work, since the foam plastic is held firmly by the steel reinforcements and can only be scraped out in small pieces.